1. Field of the Invention
The present invention relates to a lubricant applicator and more particularly, to a lubricant applicator which applies a lubricant on the surface of an image bearing member of an electrophotographic image forming apparatus. In addition, the present invention also relates to an electrophotographic image forming apparatus and a process cartridge, which include a lubricant applicator, and to a method for assembling the process cartridge.
2. Discussion of the Background
Recently, process cartridges including a unit of, for example, a photoreceptor and one or more of image forming devices such as charging devices, developing devices, and cleaning devices are broadly used for electrophotographic image forming apparatuses. Even when one or more image forming devices in a process cartridge of an image forming apparatus are damaged or the lives thereof expire, the image forming apparatus can be continuously used with a short downtime by replacing the process cartridge with new one. In this case, since only the replacing operation is necessary, the operation time of the serviceman is very short. Alternatively, a user may perform the replacing operation without calling a serviceman because the replacing operation is easy.
In order to produce high quality images using such process cartridges, it is necessary to assemble constituent members with high precision. Particularly, it is necessary to precisely contact a cleaning blade with a photoreceptor. Specifically, when a cleaning blade is not precisely contacted with a photoreceptor (for example, the pressure of the blade varies in the longitudinal direction thereof or the contact angle of the blade varies), defective cleaning is caused, resulting in formation of abnormal images such as white spots in solid or halftone images and grainy images (i.e., microscopically uneven density images).
In attempting to well remove toner particles remaining on the surface of a photoreceptor after a transfer process, a technique in that a lubricant is applied on the surface of the photoreceptor is used. For example, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2005-070276 discloses an image forming apparatus which includes an image bearing member (i.e., photoreceptor), a charger configured to charge the photoreceptor, a light irradiator configured to irradiate the charged photoreceptor with imagewise light to form a latent image, a developing device configured to develop the latent image with a developer including a toner to form a toner image, a cleaner configured to clean the surface of the photoreceptor, a transfer device configured to transfer the toner image onto a receiving material optionally via an intermediate transfer medium, and a fixer configured to fix the toner image on the receiving material, wherein a lubricant applicator is provided between the cleaner and the charger to apply a lubricant on the surface of the photoreceptor, i.e., to decrease the friction coefficient of the surface of the photoreceptor, thereby increasing the transfer rate of toner images.
JP-A 2005-018047 discloses an image forming apparatus including a cleaner configured to remove and collect toner particles remaining on the surface of a moving member, and a lubricant applicator configured to apply a lubricant on the surface of the moving member to decrease the friction coefficient thereof. The lubricant applicator is provided outside the cleaner and has a casing whose edges form an opening. The edges of the casing are contacted with the surface of the moving member to apply a lubricant, which is contained in the casing, to the surface of the moving member.
JP-A 2001-305907 discloses an image forming apparatus in attempting to prevent formation of abnormal images such as omissions, blurred images and grainy images. The image forming apparatus has an endless image bearing member configured to bear a toner image thereon, an intermediate transfer medium configured to receive the toner image from the image bearing member (primary transfer process), and a transfer device configured to transfer the toner image on the intermediate transfer medium to a receiving material (secondary transfer process). The image forming apparatus further includes a lubricant applicator configured to apply a lubricant to the surface of the surface of at least one of the image bearing member and the intermediate transfer medium, before a toner image is formed on the surface; a cleaner configured to clean the surface before the lubricant is not applied on the surface; and a smoother configured to smooth the applied lubricant.
On the other hand, in order to produce high quality images, recent image forming apparatuses include a charger applying a DC voltage overlapped with an AC voltage and use a developer including a polymerization toner. When such a charger is used, a problem in that a film of toner is formed on the surface of a photoreceptor tends to occur. In attempting to solve the problem, a lubricant such as zinc stearate is applied on the surface of the photoreceptor. When a polymerization toner is used, it is difficult to remove residual toner particles from the surface of a photoreceptor with a cleaning blade. Specifically, even when the edge of the blade is slightly damaged, abnormal images are formed. If a lubricant, a brush roller serving as the lubricant applicator and a lubricant smoother are not accidentally provided in an image forming apparatus or a process cartridge, abnormal images are formed and therefore the process cartridge has to be replaced with a new process cartridge.
When abnormal images are formed due to damage of the edge of a cleaning blade, the cleaning blade has to be replaced with a new blade. Therefore, in order to prevent formation of abnormal images, it is preferable to prevent the cleaning blade, lubricant applicator and lubricant smoother from being damaged, resulting in prevention of damaging of the photoreceptor.
It is well known that although there is a case where a photoreceptor serving as an image bearing member is damaged when image forming operations are repeatedly performed thereon, the photoreceptor is typically damaged by other devices when a process cartridge including the photoreceptor and the devices is assembled. The above-mentioned JP-As 2005-070276, 2005-018047 and 2001-305907 never discuss the point.
As a result of the present inventors' study, it is found that it is difficult to form a uniform lubricant layer only by coating a lubricant on the surface of a photoreceptor and then smoothing the coated layer with a blade. When an uneven lubricant layer is formed, the friction coefficient of the surface of the image bearing member tends to vary, resulting in formation of abnormal images such as omissions, blurred images and grainy images.
Techniques in that a lubricant is applied to the surface of a photoreceptor on an upstream side from a cleaner relative to the rotation direction of the photoreceptor are known. In this case, the applied lubricant is smoothed with the cleaner. However, the techniques have a drawback in that the quantity of the lubricant on an image forming area (on which residual toner particles are present) is different from that on a non-image area (on which residual toner particles are not present) because the lubricant adhered to the toner particles is removed from the surface. Therefore, it is hard to control the quantity of lubricant present on the surface of the photoreceptor.
Techniques in that a lubricant is applied to the surface of a photoreceptor on a downstream side from a cleaner relative to the rotation direction of the photoreceptor and a smoothing device is optionally are also well known. In this case, the problem in that the lubricant is mixed with residual toner particles can be avoided.
JP-A 2000-330443 discloses a technique in that a lubricant to be applied is set so as to be sandwiched by a cleaning blade and a smoothing member. The smoothing member is a polyurethane blade and is set under the conditions such that the smoothing member counters the image bearing member and the contact pressure and angle are 1.37 g/mm and 11.7°, respectively. The cleaning member is a polyurethane blade and is set under the conditions such that the cleaning member counters the image bearing member and the contact pressure and angle are 2.97 g/mm and 9.6°, respectively.
JP-A 2001-305907 discloses a technique in that a lubricant applicator is set on a downstream side from a cleaner relative to the rotation direction of the photoreceptor and a smoothing blade is set on a downstream side from the lubricant applicator so as to trail the photoreceptor.
JP-A 2004-354695 discloses a technique in that a lubricant applicator is set on a downstream side from a cleaner relative to the rotation direction of the photoreceptor and a smoothing brush is set on a downstream side from the lubricant applicator.
Because of these reasons, a need exists for a lubricant applicator which can uniformly apply a lubricant to the surface of an image bearing member, and a process cartridge which includes a photoreceptor and a lubricant applicator and which can be assembled without damaging the photoreceptor.